Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

Show paginator

Hide paginator

25%

Page 1 of 4

1. Freon group of refrigerants are

Non-inflammable and toxic

Inflammable

Nontoxic and non-inflammable

Toxic

2. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

3. Which of the following cycles uses air as the refrigerant?

Ericson

Stirling

Bell Coleman

Carnot

4. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

1.33

2.33

4.33

5. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Freon

Carbon dioxide

Brine

Ammonia

6. The curved lines on a psychrometric chart indicates

Relative humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

7. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

8. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Reversed Carnot

Carnot

Rankine

9. The capillary tube, as an expansion device, is used in

Water coolers

Domestic refrigerators

All of these

Room air conditioners

10. The boiling point of ammonia is

-30°C

-77.7°C

-10.5°C

-33.3°C

Page 2 of 4

11. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Any one of the above

Equal to unity

Always less than unity

12. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Evaporator and compressor

Receiver and evaporator

Condenser and receiver

13. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Refrigerant cooling tubes

Capillary tubes

Evaporator tubes

14. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

15. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

15 bar

8 bar

2 bar

16. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Normal cooling

Sub-cooling or under-cooling

None of these

Super-cooling

17. Most thermostatic expansion valves are set for a superheat of

10°C

5°C

20°C

15°C

18. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Wet bulb temperature of air

Dry bulb temperature of air

Dew point temperature of air

19. A thermostatic expansion valve in a refrigeration system

None of the above

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

20. For obtaining high COP, the pressure range of compressor should be

Any value

Optimum

Low

High

Page 3 of 4

21. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

1: 1

1: 3

9: 1

22. Cooling water is required for following equipment in ammonia absorption plant

Absorber

Condenser

Evaporator

Condenser, absorber and separator (rectifier)

23. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Same

Less

24. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Detect liquid in vapour

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

25. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

Positive

Zero

None of these

26. Rating of a domestic refrigerator is of the order of

5 tons

10 tons

40 tons

0.1 ton

27. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

28. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Above critical temperature

At critical Temperature

Much below critical temperature

29. Which of the following is not a desirable property of a refrigerant?

Low boiling point

High risibility with oil

Large latent heat

Good electrical conductor

30. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant pressure

Takes place at constant entropy

Takes place at constant temperature

Involves no change in volume

Page 4 of 4

31. The domestic refrigerator uses following type of compressor

Axial

Piston type reciprocating

Centrifugal

Miniature sealed unit

32. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.4

0.6

0.376

33. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

1.25

2.15

34. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

35. A bootstrap air cooling system has

Two heat exchangers

One heat exchanger

Three heat exchangers

Four heat exchangers

36. The freezing point of sulphur dioxide is

-77.7°C

-56.6°C

-135.8°C

-75.2°C

37. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

38. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Wet vapour

Saturated liquid

Dry saturated vapour

39. Critical temperature is the temperature above which

Water will never evaporate

A gas will never liquefy

Water will evaporate

A gas will immediately liquefy

40. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

Share this Now with Friends:

VideRime

A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

Related

Leave a ReplyCancel reply

Ads by Google

Recent Posts

Membership Registration

Secured Payment

Protection